1. Field of Application
The following description relates generally to telecommunications systems and wireless communications systems.
2. Prior Art
Cell capacity is a key performance measure in wireless cellular networks. Multipoint broadcasting and spatial multiplexing have the potential to increase cell capacity by multi-fold, and have been adopted in LTE-A (long-term evolution of 3G, advanced) under the names of co-ordinated multipoint transmission (CoMP) and multi-user MIMO (MU-MIMO), respectively.
To fully realize the benefits of CoMP and MU-MIMO, collaborating base stations must have full downlink channel information, which has to be fed back by mobile users via the uplink. The huge feedback overhead, however, diminished the uplink capacity and made CoMP and MU-MIMO not feasible to implement until recently. Highly efficient channel estimation and feedback schemes based on time-domain parameter (TDP) extraction have recently been proposed, which improve the estimation accuracy and reduce the feedback overhead by one to two orders of magnitude.
TDP extraction takes into account the fact that wireless channels generally consist of sparse multipaths. A sparse channel can be described by a limited number of the TDPs which requires a much smaller amount of data, thereby reducing the channel feedback overhead significantly.
For certain cell terrains, there may exist spots within the cellular coverage area where the wireless channels are not sparse. While such situations may be rare, they nonetheless pose problems for sparse channel-based methods such as TDP extraction. The mismatch between an overly dense channel and a sparse channel-based method degrades estimation quality and increases feedback overhead, which reduces the benefits of CoMP and MU-MIMO and lowers the cell capacity.
Thus methods, apparatus, and systems are needed that detect the sparse channels so that (a) sparse channel-based methods can be reliably and effectively employed whenever possible, (b) the performance degradation due to the mismatch is minimized, and (c) fallback approaches can be used that maximize the estimation and feedback performance and overall cell capacity under non-sparse channels.